1. Field of the Invention
The present invention relates to an aqueous developing solution and its use in providing improved development of positive-working photoresist compositions.
2. Description of Related Art
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of integrated circuits and printed wiring board circuitry. Generally, in these processes, a thin coating or film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits or aluminum lithographic printing plates or copper plates of printed wiring boards. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an imagewise exposure of radiation. This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this imagewise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.
There are two types of photoresist compositions--negative-working and positive-working. When negative-working photoresist compositions are exposed imagewise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to a developing solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-expsed areas of the resist coating and the creation of a negative image in the photoresist coating, and thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited. On the other hand, when positive-working photoresist compositions are exposed imagewise to radiation, those areas of the resist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working resist with the developer causes removal of the exposed areas of the resist coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered.
After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. This etchant solution or plasma gases etch the portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the imagewise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining resist layer after the development step and before the etching step to increase its adhesion to the underlying substrate and its resistance to etching solutions.
Positive-working photoresist compositions are currently favored over negative-working resists because the former generally have better resolution capabilities and pattern transfer characteristics.
Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of one micron or less are necessary.
In addition, it is generally desirable that the developed photoresist wall profiles be near vertical relative to the substrate and no resist residue be present on the substrate surface on the exposed and developed areas. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer onto the substrate.
The formation of a latent image on the photoresist coating by the imagewise exposure of the coating with radiant energy and the conversion of this latent image to a suitable relief image on the coating by the developer solution may be dependent upon several processing variables, including:
1. Photoresist coating thickness PA1 2. Photoresist soft baking temperature PA1 3. Radiant Energy Type (e.g., UV light or electron beam current) PA1 4. Radiant Energy Amount PA1 5. Developer Type PA1 6. Developer Concentration PA1 7. Development Temperature PA1 8. Development Time PA1 9. Development Mode (e.g., immersion or spray or both)
These parameters are frequently played against each other to balance the sometimes-conflicting goals of the overall microlithographic operation (e.g. amount of throughput, degree of image dimension control and resolution desired as well as process latitude). This parameter balancing may be aided in the case of positive-working photoresist coating if a developer solution is selected which has a rapid dissolution rate of the exposed areas of the resist coating while relatively unaffecting the unexposed areas of the resist as well as also providing good image quality, developed image dimension (DID) control and process latitude.
In the past, numerous aqueous developing solutions have been known in the photoresist art for use with positive-working resist coatings. Generally, there are three classes of these developing solutions. They are metal-containing developers, metal ion-free developers and organic solvent developers.
Known metal-containing developers include aqueous solutions of alkali metal salts such as alkali metal hydroxides, alkali metal phosphates, and alkali metal silicates and mixtures thereof. One known metal-containing developer contains the combination of trisodium phosphate sodium metasilicate in water. Known metal ion-free developers include aqueous solutions of quaternary ammonium hydroxides such as tetramethylammonium hydroxide. Known alkaline organic solvent developers include solutions of alkaline organic solvents such as mono lower alkanol amines, alkylene glycols and the lower alkyl alcohols. One known alkaline organic solvent-containing developer is made up of the combination of monoethanolamine, ethylene glycol and isopropyl alcohol.
Organic solvent developers are not favored over the two other developer types for most applications because they are very sensitive to temperature changes, thereby causing inconsistent lithographic performance. However, alkali-metal containing developers, while very stable under most processing conditions and providing relatively high resolution, have the disadvantage of leaving alkali metal ion residues which may be detrimental in some processes. Metal ion-free developers have the disadvantage of being too aggressive, thus not obtaining high resolution for certain applications.
In electron beam exposure processes and some UV light exposure processes, an aggressive development with high selectivity is needed. None of these known type developers meet this need. Accordingly, the present invention is a solution to this need.